Method of coating both surfaces of a web

ABSTRACT

A METHOD OF COATING BOTH SURFACES OF A FLEXIBLE WEB COMPRISING COATING A COLLOIDAL SOLUTION ON A FIRST SURFACE OF SAID FLEXIBLE WEB, COOLING AND GELLING SAID COLLOIDAL SOLUTION COATED ON SAID FIRST SURFACE OF SAID WEB, SUPPORTING SAID WEB WITH A STATIONARY ROLLER WHICH IS IN CONTACT WITH SAID COLLOIDAL SOLUTION ON SAID FIRST SURFACE OF SAID WEB, AND COATING A COLLOIDAL SOLUTION ON THE SECOND SURFACE OF SAID FLEXIBLE WEB WHERE SAID WEB IS SUPPORTED BY SAID STATIONARY ROLLER.

Jan. 1, 1974 HISASHI TAK|MOTQ ETAL 3,782,995

METHOD OF COATING BOTH SURFACES OF' A WEB Filed July 6, 1970 INVENTORS H|SASH\ TAKIMOTO MINORU MINODA AKIRA TAKAGI By 5%..; M ZM ATTORNEYS United States Patent O 3,782,995 METHOD OF COATING BOTH SURFACES OF A WEB Hisashi Takmoto, Minoru Minoda, and Akira Takagi, Kanagawa, Japan, assignors to Fuji Photo Film Co., Ltd., Kanagawa, Japan Filed July 6, 1970, Ser. No. 52,496 Claims priority, application Japan, July 3, '1969, 44 52 719 Inf. Cl. B44d 1/02 c U.S. Cl. 117-34 6 Clalms ABSTRACT OF THE DISCLOSURE BACKGROUND OF TH-E INVENTION Field of the invention The present invention relates to a method of coating both surfaces of a Web, and more specifically to a method of coating a colloidal solution onto both surfaces of a running web.

Description of the prior art In a conventional type of method of coating both surfaces of a running web with a colloidal solution (such as in the method of producing a photographic photosensitive material, e.g. a photosensitive material having a photosensitive emulsion layer on one surface thereof and a layer for curling balance or an anti-halation layer on the other surface thereof, or a photosensitive material having photosensitive emulsion layers on both surfaces thereof), one surface thereof is rst coated with the coating solution and after the coated solution has been dried, the opposite surface is then coated with the coating solution. Such -a type of conventional method of coating a web has various disadvantages.

Since the web is subject to two processes of coating and drying in such a conventional method, the production efficiency is low and the quality is deteriorated by twice passing the web through the drying device. The surface of the web which is coated the first time is dried twice, and accordingly, the quality of the photosensitive layer on this surface is not as high as that of the other layer. Since the time necessary for completing the entire process of coating and drying is rather long in the abovedescribed conventional method, the probability of dust sticking is high.

In order to overcome these defects as described above, another method of coating is known wherein both surfaces of the running flexible web are coated at the same time and the coated web is then subjected to the drying process without being in touch with any web feeding device such as rollers.

Furthermore, there has been devised yet another method of coating, wherein the web is fed without contact and after one surface of the web is coated and before the coated surface is dried, the opposite surface thereof is coated. According to such improved methods as described above, the time necessary for producing a web coated on both surfaces is shortened.

In such improved methods of coating, however, the technique of feeding the dlexible web without contact after the web is coated requires fairly high technical skill for stabilizing the coating process by preventing the vibration of the running web. This is particularly difficult in a method of coating a web in the process of producing photographic material wherein the thickness of the coating should be constant with high accuracy.

The principal object of the present invention is to provide a method of coating both surfaces of a flexible running web.

Another object of the present invention is to provide a method of coating a colloidal solution on both surfaces of a flexible running web, in which one surface of the web is coated with the colloidal solution after the other surface of the web is coated and before the lfirst coated surface is dried.

Still another object of the present invention is to provide a method of coating a colloidal solution on both surfaces of a flexible running web, in which one surface of the web is coated with the colloidal solution after the other surface of the web is coated and gelled, and before the iirst coated surface is dried, at a position where the web is supported by a supporting roller which is in contact with the surface of the web bearing the gelled `colloidal coating.

Other objects and advantages of the present invention will be apparent from the following description of the preferrerd embodiments of the present invention taken in conjunction with the accompanying drawing.

SUMMARY OF THE INVENTION The present invention provides a method of coating a flexible web on both surfaces thereof which overcomes the above-described drawbacks of the conventional methods. In accordance with the method of the present invention, a colloidal solution is first coated on one surface of a flexible web and then advanced to another coating position for coating the colloidal solution on the opposite surface thereof, wherein the coated solution on the first surface of the web is not dried but only gelled. The surface of the web bearing the gelled colloidal solution is brought into contact with a supporting roller at the position where the opposite surface is coated.

BRIEF DESCRIPTION OF THE DRAWING The figure shows an elevational view in section of the apparatus used for carrying out the method of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing, showing an embodiment of the apparatus in accordance with the present invention, the flexible web 1 running from the web feeding source 15 is brought to the rst coating position 2, wherein one surface a of the flexible web 1 is coated with a colloidal solution 4 by means of coating device 3. The liexible web 1, coated on one surface thereof, is further fed through a rst cold air set portion 5 while being supported by a plurality of supporting rollers 9 which are in contact with the opposite surface b of the exible web 1, whereby the coated surface a of web 1 and the colloidal solution 4 coated on surface a are cooled and gelled by the cold air forced through the ejection nozzles 16 which is supplied by cold aid duct 13 to cold air chamber 17. The temperature of the cold air varies from -10 C. to 10 C. In this cooling process, the coated colloidal solution 4 is uniformly cooled an gelled to the extent that the gelled colloid is not damaged by contact with a solid surface. Flexible web 1 is then brought to a second coating position 6. At the second coating position 6, surface a bearing the gelled colloid thereon is brought into direct contact with the surface of roller 7 which is rotatable about a stationary axis and supports the web 1, and the opposite surface of the web 1 is then coated with a colloidal solution 11 by means of coating device 10. That is, flexible web 1 is supported by roller 7 while uncoated surface b thereof is being coated.

Though the coated colloid solution 4 is not completely dried, the thus-coated surface a of web 1 is not damaged by the supporting roller 7 which is in contact with coated surface a at the second coating position 6. This is believed to be due to the increase in solution concentration, the increase in jelly strength by cooling, the lubrication occurring by the liberated water content on the surface of the jelly, and the like. Accordingly, the concentration of the solution to be coated should be selected in view of the resulting jelly strength and the amount of water which is liberated. Generally, the concentration of the colloidal solution varies from to 20 weight percent.

The colloidal solutions 4 and 11 coated on both surfaces of web 1 are then cooled and gelled in a second cold air set portion 8 after both surfaces of web 1 have been coated. After both surfaces of web 1 are coated, web 1 is brought into the drying portion 12 by a web feeding system which feeds the web without contacting the same. The cold air is exhausted through duct 14 after the air is used for cooling web 1.

As the flexible web 1 in the case of photographic photosensitive material, cellulose triacetate, polyethyleneterephthalate, polystyrene, polycarbonate or polyolefin Webs, and the like, having a thickness of from 50 to 300M are generally used. The coating devices 3 and 10 used for coating the colloidal solution onto the flexible web 1 at the coating positions 2 and 6 may be of any type conventionally known. Of course, a multi-layer coating device can be used as the coating device 3 or 10. The thickness of the colloidal layers varies from 0.05 mm. to 0.15 mrn.

The colloidal solutions 4 and 11 to be coated on the surfaces of the ilexible web may be any type of colloidal solution, such as gelatinous silver halide, a gelatin solution used to protect an emulsion layer, a gelating solution used for an anti-halation layer in the case of photographic material, etc. As for the cooling means used in portions 5 and 8, cold air is only an example of a single means for cooling the web, and it should be understood that any type of cooling means such as cooling Water and other suitable cooling media can be employed, so long as the coated web is cooled suiiiciently to gel the colloidal solution coated onto the web 1. Furthermore, it is apparent that means for accelerating the coagulation of the coated material by chemical reaction can be employed for cooling and gelling the coated colloidal solution on the web. It is important for the colloidal solution to have a sufiicient jelly strength and not to have a high degree of fluidity so that when the colloidal solution is cooled and gelled on one surface of the web 1, it may not be damaged when the coated surface of the web is brought into contact with the supporting roller after being coated but before being completely dried.

In other words, the colloidal solution changes from a sol condition to a gel condition.

The coating device and the colloidal solution 11 to be coated on the uncoated surface b of the flexible web 1 at the second coating position 6 lmay be the same as Were employed at the first coating position 2. Further, the surface of supporting roller 7 is preferably smooth enough so as not to damage the surface of the colloidal solution layer 4 which has been gelled on surface a of flexible Web 1. The supporting roller 7 is preferably made of stainless steel, and the like, from the view point of accuracy in dimensions, `but it might be desirable to provide a lining of Teflon, or the like, thereon in order to prevent sticking and to provide ease of separation between the coated surface of the web and the surface of roller 7.

The advantageous features of the present invention are due to the fact that the coating in accordance with the present invention utilizes the characteristic of the colloidal solution that the colloidal solution, after being coated on the flexible web, is not damaged by external mechanical operations and has enough elasticity to recover its original shape after removal of the external pressure after the colloidal solution is gelled, and that the colloidal solution coated on the web may have a surface layer of liberated water content which serves as a protector for the colloidal layer and also functions as a lubricant between the colloidal layer and the surface of the roller.

In the prior art, it has been regarded as impossible to bring the colloidal solution layer into contact with a solid surface even if the colloidal solution is cooled and gelled. In the present invention, however, the contact between the gelled colloidal solution and the solid surface is made possible. According to this improved state of the art, the present invention provides several advantages as follows.

First, since a continuous coating on both surfaces of the web is possible, the production efficiency is remarkably improved, and accordingly there is no need to store the uncompleted products or carry them in the long process of production. This lowers the cost of producing the coated products and decreases the possibility of damaging the products during production. Of course, these advantages improve the quality of the products.

Second, since it is possible to use the back up roller or supporting roller at the second coating position, the feeding of the flexible web is easy and certain. This contributes to the improvement of the products particularly to a constant coating thickness and a uniform coating quality. That is, vibration of the flexible running web is prevented by the supporting roller, which results in a uniform coating of the solution.

Third, since the gellation of the colloidal solution on the web after coating is made by cooling the single surface of the web, the gellation of the colloidal solution is performed faster than the case wherein the opposite surface of the web is cooled at the same time. Accordingly, the effect of the drying process is also improved.

Four, since the drying process is conducted only once for each surface of colloidal solution coating, there is no deterioration in the efficiency of the coated material on the web as seen in the conventional method wherein one surface with a coating thereon is passed through a drying portion twice in the process.v

The present invention will be illustrated further by reference to the following non-limiting examples.

EXAMPLE I In a process for making lithographie printing tlilm, cc./m.2 of a gelatin solution was coated onto one surface of a flexible web at a first coating position to thereby form a curling-balance and anti-halation layer. At the cooling position adjacent to the first coating position, the resultant coated solution was gelled by means of cold air at -3 C. After the coated solution was gelled by the cold air, the flexible Web was supported on the coated side by a roller, maintained at a temperature (0 C.) which will not affect the coated colloidal solution, at the second coating position. The coated side of the flexible web was in contact with the supporting roller. The opposite uncoated surafce of the web was coated first with 85 cc./m.2 of a gelatinous silver halide emulsion solution and then with 25 cc./m.2 of a gelatin solution as a protection layer, superimposed over the first layer. After the two solutions Were coated, cold air at a temperature of 4 3 C. was used for cooling and gelling the second coated solution. Then both coated surfaces of the flexible web were dried. The film thus produced had good quality and no damage on the coated layer was recognized on the side of the web Which was coated first.

EXAMPLE II In a process for making office-use copying film, 85 cc./m.2 of a gelatinous silver halide emulsion solution was coatedon a lirst surface of a flexible web and then cooled by means of cold air at 3 C. After the coated solution was cooled and gelled, the coated surface of the web was brought into contact with a stationary supporting roller where 85 cc./m.2 of a gelatin solution was coated on the opposite surface of the web to form a curlingbalance and anti-halation layer. After the solution was coated on the second uncoated surface, the resulting coated surface was cooled and the coated material thereon was gelled by means of a cold air at 3 C. Then, both surfaces of the web were dried. Good results were obtained, as in Example I.

What is claimed is:

1. A method of coating both surfaces of a flexible web consisting essentially of coating a colloidal solution on a rst surface of said exible web, cooling and gelling said colloidal solution coated on said rst surface of said web until water is liberated on the surface of the gelled solution to form a water surface layer, supporting said web on a roller which is disposed in contact with the Water covered gelled colloidal solution on said rst surface of said web, and coating a colloidal solution on the second surface of said flexible web while said web is supported by said roller, cooling and gelling said coating on said second surface and drying both surfaces of said coated flexible web.

2. A method as in claim 1, wherein said colloidal solution is a gelatin solution.

3. A method as in claim 1, wherein said colloidal solution is a gelatino silver halide emulsion.

4. A method as in claim 1, wherein the concentration of said colloidal solution varies from 5 to 20 Weight percent.

5. A method as in claim 1, wherein the thickness of each of said coatings varies from 0.05 mm. to 0.15 mm.

6. A method as in claim 1, wherein said cooling is performed by subjecting the coated. web to cold air at a temperature of from '-10" C. to 10 C.

References Cited WILLIAM D. MARTIN, Primary Examiner W. R. TRENOR, Assistant Examiner U.S. Cl. X.R. 

